1. Field of the Invention
The present invention relates to a magnetoresistive head and, more particularly, to a magnetoresistive head having a spin valve MR film for use in a magnetic sensor, a magnetic head or the like.
2. Description of the Prior Art
In the magnetic sensor or the magnetic head, a magnetoresistance layer employing NiFe as magnetic material has been used. According to an increasing requirement for higher sensitivity of the magnetic sensor or the magnetic head, a GMR (Giant Magnetoresistance) film from which one can read large amplitude signals has been watched with interest. In particular, since a spin valve magnetoresistance film can be relatively readily fabricated and it has a large change rate of electric resistance in a low magnetic field in contrast to the conventional one, such film has recently been given much attention.
Devices using a spin valve magnetoresistance effect have been proposed in U.S. Pat. No. 5,206,590, for example. These devices have structures as shown in FIGS. 1A and 1B, for example.
In FIGS. 1A and 1B, in a magnetic field having specific magnitude, a backing layer 2, a first magnetic layer 3, a nonmagnetic metal layer 4, a second magnetic layer 5, and an antiferromagnetic film 6 are formed on a silicon substrate 1 by a sputter method. All layers from the backing layer 2 to the antiferromagnetic film 6 are patterned to have a rectangular shape. In addition, a pair of conductor leads 7a, 7b are formed at a distance in the longitudinal direction on antiferromagnetic film 6.
Materials constituting these layers, for example, tantalum (Ta) as the backing layer 2, iron-nickel (NiFe) as the first and second magnetic layers 3, 5, copper (Cu) as the nonmagnetic metal layer 4, and iron-manganese (FeMn) as the antiferromagnetic film 6 may be used.
Using the above, the spin valve magnetoresistive head has been completed.
The first magnetic layer 3 has rectangular magnetization M.sub.a in the longitudinal direction. The second magnetic layer 5 can be magnetized by being coupled with the antiferromagnetic film 6. A direction along magnetization M.sub.b is one direction of a short side of the rectangular shape. A signal magnetic field H.sub.sig derived from a magnetic recording medium is generated in the direction of the short side of these layers. When the signal magnetic field H.sub.sig is applied to the magnetoresistance transducer, the direction of the magnetization M.sub.a of the first magnetic layer 3 is caused to be inclined according to strength and direction of the signal magnetic field H.sub.sig.
A component of the magnetization M.sub.a of the first magnetic layer 3, which is in the opposite direction to the magnetization M.sub.b of the second magnetic layer 5, serves as a primary factor to scatter electrons passing through these layers and thus increase the electric resistance of all layers. In contrast, since a component of the magnetization M.sub.a of the first magnetic layer 3, which is in the same direction to the magnetization M.sub.b of the second magnetic layer 5, does not scatter electrons passing through these layers, the electric resistance of all layers is decreased.
The electric resistance in sense current areas is varied in proportion to a cosine of a relative angle .theta. between the magnetization M.sub.a of the first magnetic layer 3 and the magnetization M.sub.b of the second magnetic layer 5, i.e., cos .theta..
In order to change the electric resistance linearly against the signal magnetic field H.sub.sig derived from the magnetic recording/reproducing medium, the magnetization M.sub.a of the first magnetic layer 3 is intersected orthogonally with the magnetization M.sub.b of the second magnetic layer 5 in a state of zero signal magnetic field. The signal magnetic field H.sub.sig must be applied in the direction either identical to or opposite to the magnetization direction of the second magnetic layer 5, i.e., the fixed magnetization direction.
In the case the signal magnetic field H.sub.sig derived from a magnetic recording/reproducing medium is to be changed into an electric signal, change in electric resistance due to the signal magnetic field H.sub.sig can be transformed into change in voltage by flowing a constant electric current between the pair of conductor leads 7a, 7b. The change in the voltage is used as a reproducing electric signal.
In the meanwhile, in the device employing NiFe as material of the magnetic layer in which the spin valve magnetoresistance effect is caused, the change rate of electric resistance by the signal magnetic field is as small as 2.5%. Therefore, the device is insufficient for the magnetic sensor or the magnetic head of high sensitivity.